Because of the increase in communications and data handling and the increase in operating systems for handling these, it is becoming increasingly important to raise the frequencies at which the various systems operate. To raise the frequencies of the operating systems, it is necessary to increase the upper or maximum frequencies of the devices used in the various systems.
In one example, heterojunction devices, such as heterojunction bipolar transistors (HBTs), can be made very small, which greatly reduces internal capacitances, such as intrinsic base-collector capacitance. However, because external base contacts must be made large enough for low resistance external contact, the extrinsic base-collector capacitance is usually 10-15 times as large as the intrinsic base-collector capacitance and substantially reduces the maximum frequency of the device.
Accordingly, it is highly desirable to provide a bipolar transistor with a lower extrinsic base-collector capacitance, or higher maximum operating frequency.
It is a purpose of the present invention to provide a new and improved bipolar transistor.
It is another purpose of the present invention to provide a new and improved heterojunction bipolar transistor with substantially reduced extrinsic base-collector capacitance.
It is a further purpose of the present invention to provide a new and improved bipolar transistor with a substantially increased maximum operating frequency.
It is still a further purpose of the present invention to provide a new and improved bipolar transistor with a substantially increased maximum operating frequency fabricated by a highly controllable process.